Not All Rocks are Pond Rocks: Choosing the right stones to rock your pond project

Published on July 1, 2013

Lava rock samples.
Lava rock samples.

Since the beginning of time, rocks have been our oldest historians. Some of them are over 3.5 billion years old. They come in many sizes, shapes, ages, colors and weights. Classified into three main groups or types, they are: Sedimentary, Metamorphic and Igneous.

It should be noted that each type of rock has a different degree of hardness. You should check with your local rock expert to see what is best suited for your project and environment.
Let’s start with a brief description of each.

Sedimentary rocks consist of layers: particles of sand, shells, fossils and other smaller rocks we know as sediment. After billions of years, these layers of sediment have compressed into rock. In some cases, these rocks are softer and may crack or crumble depending on the weather and their use. The weather should play a big part in your selection, so keep this in mind when selecting rocks.
Some examples of sedimentary rocks are Limestone, Sandstone and Siltstone. These are widely used for pond-building in Central Texas because of the temperature. Sandstone and limestone are the softest of the sedimentary rocks.

Metamorphic rocks are formed underground under intense heat and pressure and after billions of years the effect or look can be quite unique. Marble and slate are some examples of this harder rock.

Igneous rocks are molten rocks (also known as magma) very deep inside the Earth. For billions of years these rocks have been heating and cooling and rising closer to the surface. Sometimes, when there is an eruption in the form of a volcano, the rock that is produced is Lava. Lava rock and granite are very common igneous rocks.

When it comes time to look for rocks for a water garden project, most people get them either before or after the hole is dug. Of course this depends on you. Note: Before you start handling rocks you should be wearing work gloves, eye protection and some type of back support. When picking out rocks you should be prepared to move them more than one time. One pinched finger or crushed hand can ruin your whole day. Also, when buying rock you should buy by the ton, not by the pound. It should be cheaper.
Will the pond be made with concrete or an EPDM liner? Your budget will decide this question. If you can afford concrete, I believe it’s the best way to go. If not, EPDM liners are much more affordable and are almost as good.

EPDM Pond Liner:

Before you pick up your first rock, decide the style of rock- work you plan to use. Will it be the All Natural Dry-Stack look or will the rocks be cemented together — or a little of both? This is a very important question you need to ask yourself. Will your rock- work style (your coping or edging, veneering, creek or waterfall) be safe for children, pets or yourself when walking or climbing on them?
When building a pond, in terms of water handling and architecture, think simplicity and ease of maintenance. Rocks native to your area should create a more natural look for your pond.

Rock setting options

Pro: An all-natural look can be most beautiful if done correctly, as it can look like it was there before the house was built.
Con: In most cases you will be using bigger, heavier rocks — and more of them. These rocks can become loose or wobbly, and loose rocks can fall into the pond and damage it. A lot of exposed liner may be seen if the pond is not properly leveled at construction. This has been my experience when repairing ponds with the all-natural look.

Pro: When done correctly the pond is cleaner, stronger and safer — and you use less rock. Rocks bond or stick well to concrete and may need fewer repairs to the rockwork over time.
Con: Concrete will not bond or stick to the pond liner because the liner is too smooth. For concrete to work well it needs something to adhere to, like other rocks. Recently patented RockToRubber is an anchor which will provide that necessary bonding.

Over the past 30 years I have built a few ponds and repaired many. The majority of these ponds were built using sedimentary and metamorphic rocks. I believe this is due to the location of the rocks and mining cost. In general, sedimentary rocks are above the surface and metamorphic and igneous are beneath.
When dealing with rocks, remember: be patient, be careful and have fun.

1 thought on “Not All Rocks are Pond Rocks: Choosing the right stones to rock your pond project”

  1. I put marble chips at the bottom of the pond and the water turned white. What can I do to solve this problem?

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